This invention relates to the separation of isotopes such as those of uranium having different masses. In particular, the invention relates to a method by which an ionized substance can be separated into respective isotopes in accordance with the mass difference in the combination of a magnetic field and an electric field composed of a pulsating voltage superposed on a fixed voltage, as well as an apparatus for implementing the method.
The isotope separation technology has so far been largely developed to meet the need for enriching uranium-235 as a nuclear reactor fuel. Recently, it has been proposed that only the isotopes of metal elements having low activation characteristics that are relatively preferred for structural materials of nuclear fusion reactors, large-scale accelerators, etc. should be separated for use. This is because the selective separation and use of the required isotopes facilitates the maintenance of fusion reactors and large-scale accelerators and achieves considerable reduction in radioactive wastes to be disposed of. To obtain these benefits, it is required to develop a technique that is capable of separating the isotopes of metal elements at low cost.
Methods that have heretofore been used to separate uranium's isotopes and other atoms or molecules having small mass differences include gaseous diffusion, centrifugal separation, chemical approach (adsorption), mass separation in an electromagnetic field, and selective ionization with laser beams.
The gaseous-diffusion, centrifugal separation and chemical process share the common problem of an extremely low separation factor per stage (process), requiring a number of stages to be implemented in practical applications.
The mass-separation process using an electromagnetic field achieves high separation factor but, on the other hand, due to its operating principle which is based on single-particle loci in high vacuum, the throughput of the process is extremely small. The process also involves instrumental problems as exemplified by the need to limit the initial velocity and direction of ions to certain ranges for attaining the necessary resolution or to provide beam limiting slits.
The selective ionization method with laser beams, as it is applied to uranium separation, comprises illuminating a uranium atomic beam with dye laser light to achieve selective excitation of uranium-235 while, at the same time, other laser light is applied to further ionize the uranium-235. This method has met with success in uranium separation; however, with the scarcity of data accumulated for the isotopic separation of other elements; the method has no general applicability.